Abstract

Production of sporangia by Phytophthora cinnamomi. Phytophthora cryptogea, Phytophthora citricola, Phytophthora drechsleri and Phytophthora nicotianae var. nicotianae on Miracloth discs was compared in filter-sterilized and non-sterile lcachates extracted from a pine-bark based container medium (NM) and a composted Eucalyptus-bark medium (CEB). Sporangial production of all species was suppressed in non-sterile CEB leachate; whereas, in sterile CEB leachate it was stimulated in comparison to the NM leachate. P. drechsleri and P. cryptogea appeared to require the presence of certain microorganisms to induce zoospore release. Chlamydosporc production by P. cinnamomi was suppressed in CEB lcachates. On cornmcal and water agar mixed with filtcr-stcrilized or non-sterile leachate from NM and CEB. mycelial growth varied with leachate. agar type and Phytuphthora species. Isolates within P. drechsleri and P. cinnamomi responded differently to the extracts.